1. Field of the Invention
The invention relates to destemming of tobacco leaf and, more particularly, relates to apparatus and processes for the separation of tobacco leaf lamina from tobacco leaf stem.
2. Brief Description of the Prior Art
Hand stripping of leaf lamina from stems gives an ideal product, i.e., two very large strips of leaf lamina and a perfectly clean stem. Unfortunately, however, hand labor is impractical from a cost standpoint for a commercial destemming process.
Conventional leaf threshing, as currently practiced commercially, comprises various methods and apparatus for beating the tobacco leaf in order to effect a separation of stems from leaf lamina in large quantities; see, for example, U.S. Pat. No. 2,941,667. Unfortunately, conventional threshing, as currently practiced commercially, devalues some usable leaf strip by converting it to dust and very small particles. Further, as stated in U.S. Pat. No. 2,941,667, "For a thresher to strip lamina from the stem in the most efficient manner, the moisture content and temperature of the tobacco must be controlled to an ideal degree." In fact, the commercially employed method of separating tobacco leaf lamina from the leaf stem comprises taking the whole leaf from storage conditions (where it generally has a moisture content of from 8 to 13 percent) and conditioning the leaf with steam and water spray to bring the moisture content up to about 21 percent at 120.degree.-160.degree. F. The humidified leaf is then threshed and the threshings separated a number of times (at least three separate threshings and separations). The finally separated lamina and stem remnants are then dried, screened and air separated. The stem remnants are sized and dried further to be used for reconstituted sheets, etc., and the lamina remnants are sized and dried to a moisture content of 11-15 percent for future use in smoking products.
By the method of our invention, the leaf lamina is mechanically separated from the tobacco leaf stem without the need for preconditioning the leaves to obtain high moisture contents, nor is it necessary to carry out the separation at elevated temperatures. For this reason, the method of our invention is energy saving, as well as more efficient, in that fewer procedural steps are required than in the commercially practiced threshing procedures. Further, the lamina product of the process of our invention approaches a quality hitherto only available by hand stripping of the leaf lamina.
Prior to the present invention, apparatus, including so-called "stripping rollers," were employed to destem tobacco leaf; see, for example, U.S. Pat. Nos. 591,436 (1897) and 661,199 (1900). The apparatus described by these early patents are operated, essentially, by first placing the tobacco leaves in a partitioned conveyor belt. This first step is basically a hand operation and limits the effectiveness of the overall process. A mechanical stop holds the emplaced leaves on the moving conveyor belt until the previously fed leaves are delaminated. From the conveyor belt, the butts of the leaves are first drawn from the conveyor by engagement in the nip of a first set of feed rollers, which are rotating to move materials in the desired direction of leaf travel. The drawn leaves pass through an open, second set of rotating stripping rollers until the butt of the leaf reaches a third set of drawing rollers. Up until this point, the stripping rollers have been rotating to carry the leaf in the desired direction of the leaf travel. Once the butt is engaged with the drawing rollers, the stripping rollers close on the leaves passing therethrough and reverse their direction. Simultaneously, the driving rollers pull the stem away from the severed leaf lamina which then falls free. The stem is passed to additional roller pairs which engage the stem and assure its movement away from the apparatus and residual lamina.
In U.S. Pat. No. 1,842,868 (1932) another apparatus for tobacco leaf destemming is described. Whole tobacco leaves are again hand fed, butt first, on a conveying table. It is necessary that the stems be placed at right angles to the movement of the conveyor. As the leaves progress forward, a series of card cloth felts and/or overhead metal guides holds the leaves down on the conveyor. In one version, a preliminary butting operation must take place. A rotating wire brush strips some of the lamina from the butt end of the held down leaf. The leaf, now with a clean butt, passes on to a narrow card cloth conveyor. Here the lamina is stripped back by a wire brush while the stem is pulled away from the strip by a pair of facing conveyors. These conveyors are mounted at right angles to the flow of tobacco on the side of the stripper. In still another version, the butting operation is done away with. The facing (card cloth) conveyors are slightly less than at a right angle to the directional flow, allowing for a more gradual entrance of the stem into the take-away conveyors.
Those skilled in the art will appreciate that the prior known tobacco leaf destemming apparatus are not completely satisfactory for a number of reasons. For example, as described above, their operation still requires a great deal of hand labor. Further, the prior art apparatus is rather complicated, subject to breakdown, and limited in through-put rates. In addition, the use of card cloth and wire brushes damages the tobacco leaf lamina.
The apparatus of the present invention is an improvement in the art in that it provides for higher throughputs and will accommodate overlapped, padded leaves, regardless of the position of one leaf to another. It is also not necessary to butt feed tobacco leaves to the apparatus of the present invention, good results being obtained even with tip feeding. For that matter, anything other than an exact sideways orientation of the tobacco leaf gives good stripping results in the apparatus of the present invention. This eliminates hand labor for orienting the leaves. Further, the apparatus of the present invention is fully continuous and mechanically quite simple and foolproof in operation. Since the apparatus of the present invention employs elastomeric rollers, there is minimal tearing of the tobacco leaf and minimum clogging of the apparatus with small pieces.
In summary, the apparatus and process of the present invention approach the results obtained by hand stripping, but without the time and labor consumption required in hand stripping. For example, by using the apparatus of the invention it is possible to remove up to 96 percent of tobacco leaf lamina in a single pass of a given leaf through the apparatus of the invention. Sixty percent of the lamina so removed is of a size retainable on a 1-inch screen. The stripped stem remains intact in almost all instances and is easily separated undamaged. A further advantage of the apparatus of the present invention resides in the fact that its higher speed of conveying and stripping will shake off undesirable sand and foreign materials, reducing the need for later separations of these undesired contaminants.
The advantage of the method and apparatus of our invention is a reduction in tobacco loss and a finer quality tobacco product after destemming.